I've heard about people cutting slits and holes in the line, so nice that you posted it working. Thanks.
Yeah, it actually works really well. I'd say the hole is probably ~1/4" or so. I'm using a 50W Hydor submersible heater in there (AHY00034) that fits perfectly. I could have gone with the 25W since they are exactly the same size, but I went for the 50. It's a bit overkill, but rarely cycles on.